Drosophila melanogaster females, when exposed to two males of contrasting genotypes, have a particular probability of accepting one genotype over the other as a mate. Data are presented to show that the probability of a female accepting a particular mate can be dramatically altered if the female has had a prior copulatory experience with one or the other type of male. Modification of mate preferences by early copulatory experience appears to be a form of learning. Experiments are proposed to determine the key behavioral elements required for the experience effect to take place and to assess the roles of environmental and genotypic variation on the manifestation of the experience effect.